Preparation of low molecular weight organic esters



United States Patent 3,036,119 PREPARATION OF LOW MOLECULAR WEIGHT ORGANIC ESTERS Theodore Augur Koch, Glen Mills, Pan, and Ivan Maxwell Robinson, Wilmington, Del., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Oct. 1, 1959, Ser. No. 843,639 14 Claims. (Cl. 260-486) This invention relates to a process for preparing organic esters,'and more particularly to a process for preparing low molecular Weight organic esters of monocarboxylic acids from monoesters of dicarboxylic acids.

Low molecular Weight organic esters may be prepared in a variety of ways. Acrylic esters have received special attention due to their usefulness as monomers to prepare solid thermoplastics. One method of preparation involves the carbonylation of acetylene. Another method which has been proposed involves preparing acrylic acid by pyrolysis of maleic acid in the presence of steam and subsequently esterifying the recovered acrylic acid. This latter method has not achieved commercial importance.

It is an object of this invention to provide a method of preparing low molecular weight esters of monocarboxylic acids from monoesters of unsaturated dicarboxylic acids. It is another object of this invention to provide a process which produces said esters of mono-carboxylic acids in high yields over a wide range of conversions. It is a further object of this invention to provide a process which produces said esters of monocarboxylic acids in a very pure state. It is still another object of this invention to provide an economical method of producing acrylic esters. Other objects will appear hereinafter.

The objects of this invention are accomplished by contacting at a temperature in the range of 200 C. to 550 C. a monoester of a dicarboxylic acid wherein the ester radical is derived from an alcohol containing 1 to 7 carbon atoms and the acid radical is derived from an acid selected from the group consisting of maleic acid, succinic acid, fumaric acid, mesaconic acid, itaconic acid and citraconic acid with at least one catalytic compound selected from the group consisting of metal phosphates and metal oxides wherein the metal is selected from the group consisting of the metals of groups LB, II, IV, V-A, VI-B, VII-B and VIII of the periodic table.

In general, the reaction may be carried out by passing the vaporized starting materials over a catalyst bed, condensing the products and separating the products by distillation or the like. For example, methyl acrylate may be prepared from monomethyl maleate using zinc oxide catalyst, according to the following reaction scheme:

As can be seen from the above equation, the reaction is a decarboxylation of the monoester of the di'basic acid to give the ester of the monobasic acid. If desired, the reaction may be carried out in the presence of excess of such alcohol as was used in the formation of the monoester.

The invention is operable over an extremely broad range of temperature, but it is generally desirable to operate the process at a temperature in the range of 200 C. to 550 C. In a preferred embodiment, the process is carried out at a temperature in the range of 250 C. to 450 C.

Starting materials useful in the process of this inven-' tion are prepared from the reaction of analcohol with a dicarboxylic acid or anhydride. Useful alcohols in- 3,035,l l9 Patented May 22, 1962 Chemistry by Sneed and Maynard, published by D. Van

Nostrand Company, New York (1942). As used herein, the metals of group II-A include Be, Mg, Ca, Sr, Ba and Ra; the metals of group IV-A include Ge, Sn and Pb; the metals of group V-A include Sb and Bi; the metals of group I-B include Cu, Ag and An; the metals of group II-B include Zn, Cd and Hg; the metals of group IV-A include Ti, Zr and Hf; the metals of group VI'B include Cr, Mo and W; the metals of group VIII include Fe, Ru, Os, Co, Ra, Ir, Ni, Rd and Pt. If desired, a mixture of two or more of the oxides or phosphates of these metals can be employed. It is also convenient, but not necessary, to employ an inert support for the metal oxide or phosphate. Many of the catalyst supports known in the art such as, for .example, alumina, silica gel, quartz and the like may be employed. The preferred phosphates and oxides are those of Zn, Co, Cr, Mg, Mn, Fe, Ni and Cu.

The method of contacting the catalyst and starting material is not critical, and any of the methods known in the art for contacting a fluid and a solid are generally useful. The contact times for this reaction can be varied over an extremely broad range, the preferred range being 0.2 sec. to 300 sec. Contact times to achieve the same conversion decrease with increasing temperature. Optisult in the most desirable combination of yield and conversion will difier for any given reactor, but can be easily determined by those skilled in the art.

The pressure at which the reaction is carried out is not critical. It is preferred to carry out the reaction at ambient atmospheric pressure, but subatmospheric pressure or superatmospheric pressure may be employed if desired.

In order to more clearly illustrate our invention, the preferred modes of carrying out the same, and the advantageous results to be obtained thereby, the following examples are included. Unless otherwise stated, all parts and percentages herein are by weight.

As used herein, the terms percent yield, percent conversion and percent production mean:

Percent conversion total moles of starting materials converted to products total moles of starting material supplied Percent yield moles of the given productX moles of starting material theoretically required to form one mole of the given product Percent production: 100

EXAMPLES I TO XXVII The starting material, shown in the tablev below, was

contacted with the catalyst by permitting the starting material to flow from a dropping funnel into the top of a vertical tube packed with quartz and the catalyst. The tube, 30 inches long and 22 mm. inside diameter, was made of mum conditions of temperature and contact time to rea o a high-silica glass. The upper 10 inches or the tube were packed with 2 to 4 mesh quartz and immediately below the quartz was placed a 10 inch bed of the catalyst indi. cated. The tube was suspended in a vertical electric fur- By comparing Examples 1 to XXIV and Examples XXV to XXVlI, it is apparent that a catalyst is required to affect the reaction. The examples further show that the process is operable over an extremely wide range of temperatures nace. Reaction temperature was measured by means of 5 and contact times to give excellent yields. The products a thermocouple attached to the outside of the tube. As which were obtained contained only trace amounts of imthe starting material contacted the quartz packing, it was purities. Since the starting material can be separated from vaporized and heated to the desired reaction temperature. the products very easily, it is apparent that the process The vaporized material was passed through the catalyst can be used to prepare extremely pure products without bed where the reaction occurred. A nitrogen carrier gas further purification. at the rate of 10 to 100' mil/min. wasted into the reaction Substantially the same results are obtained as in Examtube along with the starting materials to aid in passing pics I to XXIV by substituting as a catalyst other metal the reactants through the catalyst bed. The products and oxides or phosphates of the metals of groups I-B, 11, IV, the unreacted starting materials were passed into a water V-A, VI-B, VII-B and VH1 of the periodic table. Subcooled condenser, condensed, and collected in a receiver. stantially the same results are also obtained by substituting Uncondensed materials were vented with the carrier gas. as' a starting material in Examples I to XXlV a mono- Catalysts used in the examples illustrated in the table ester of a dicar-boxylic acid which is derived from an were generally used on a support. Metal phosphates were alcohol containing 1 to 7 carbon atoms and maleic acid, applied to the support as an aqueous solution. Altern-atesuccinic acid, fumaric acid, mesaconic acid, itaconic acid ly, the phosphate catalysts may be prepared by double or citraconic acid. While a catalyst support is not necesimpregnation of the support by a soluble salt of the metal sary, it is desirable to employ a support, since it provides followed by treatment with a solution of ammonium phosa catalyst bedwith good physical properties and generally phate. The water was driven oil by heating at 250 C. permits the use of a smaller amount of catalytic material. for 2 hours. Metal oxide catalysts were prepared by ap- The foregoing examples are not intended as limiting plying a water soluble metal salt to the support and conthe scope of the present invention, but are only illustrayerting the salt to the oxide in situ. When metal chloride tions thereof. It should be apparent that the process is solutions were used, the chloride was converted to the oxide very versatile, and many modifications will be apparent to by washing with ammonium hydroxide and subsequent one skilled in the art without departing from the spirit of heating at 250 C. for 2 hours. When metal nitrate soluthe invention. Thus, although the examples show the tions were used, the nitrate was con 'erted to the oxide by use of approximately ambient atmospheric pressure, it is heating at 400 C. to 500 C. for 2 hours. clear that the reaction can be carried out at subatmos- A summary of the results of Examples I to XXVII appheric or superatmospheric pressure if desired. Mixtures pears in Table I. Column 2 gives the starting material of metal oxides and phosphates may be used if desired. and column 10 gives the major product. Other columns In general, it is not necessary that the catalyst be of high list reaction conditions, catalysts and the like, as indipurity. The presence of sma amounts of impurities does cated. In some of the examples, the reaction was carried not materially affect the reaction. Likewise, it is not out'in the presence of excess alcohol used to form the ester. necessary that the starting material be of high purity.

Table I M01 Reac- 0011- Per- Per- Ex. Starting material ratio Catalyst cone. based on Catalyst preparation tion tact Main product cent cent alcohol weight of support temp., time, producyield ester C. sec. tion 1,.-- Monomethyl male- 11.3 10% BaO, 2.5% CuO on 14.20 mesh silica gel irn- 250 20 Methyl acrylate... 89 90 ate in methanol silica gel prletgnated with nitrate 11.3 ..;,d0 do 300 1.8 .do 14 11.3 10% CuO on silica gel Inllprrggnated with Cu- 450 8 d0 18 33 11.3 10% FePOl on silica gel. Impreguated with Fe 390 .do 92 (N093 then treat with ammonium phosphate d0 3.6 .....do d0 7 390 25 do 52 .1 Monoethyl maleata. 8.4 do d0 400 32 Ethyl acrylate- 17.5 Monomethyl male- 11.3 10% (la-P09: on silica Impregnate gel with Ca 300 8 Methyl acrylate 11 ate gel (Noah followed by ammonium phosphate 8.4 10% Fe (PO4)2+1% Ba Impregnate with BaCNO h 350 25 .do 36 (PO92 on silica gel and FeClQ, followed by phosphate treatment 11.3 10% F9203 on silica gel Impregnate' with F0013 400 4 followed by treatment with NH40H soln 16. 65 10% CdO on silica gel As in 9, using CdClz 400 40 16. 65 10%1Z11O(PO4)2 on silica As 4, using Zn(NO )1 350 12 go so n V 16.65 10% ZnO on silica gel As in 9, using Z1101: soln- 350 40 16.65 do Impregnate with Zn(NO )2 350 20 and calcine in ZnO 13. 4 do As in 12 above 250 130 13.4 10%1 132.3(PO4)2 on silica As in 4, using BG(NO3)z 300 12 as 13. 4 10% MnO on silica gel As in 9, using MnGlz 300 30 13. 4 10% N10 on silica geL. Asin 9, using NiCl2. 275 30 13. 4 10% 000 on silica gel As in 9, using 0001; 275 16 13. 4 T102, no support By hydrolysis of Ti(SO4)2 350 20 13.4 10% 01203011Sill08. gel Implregnate with 01-20 250 20 so n do 13.4 10% MgO on silica gel As in 9, using MgClz l. 325 12 clo 6'8 22. Mcnomethyl citra- 17.0 10% FB3(PO4)2 on silica gel- As in 4 above 450 22 v Mlethyl methacry- 10 00118 8: B 23-.. Monomethyl suc- 15.3 do r 400 16 Methyl propio- 9 cinate nate 24--- Moglomethyl male- 1. 01 10% ZnO on silica gel As in 9, using ZnOh 300 40 Methyl acrylate 34 a 8 25..- do 11.3 30% KHPO4 on silica gellmrrgguafegel with KHg- 400 8 do 4 S0 11 26--- do 16.65 silican carbide. 350 22 -do l 27.-. do 16. 65 10% K01 on silica gel Asin24, using K01 suln 300 30 do The presence of large amounts of water may, however, lead to the formation of acids instead of the correspond-1 ing ester.

The process of the present invention is useful in producing methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, methyl propionate and ethyl propionate in commercial quantities. The acrylates and methacrylates are useful in the production of high molecular weight polymers which have many well-known industrial applications. Acrylates and methacrylates are also useful in the manufacture of coatings, lacquers, glazing and the like. The propionates have a variety of uses including use as intermediates to make sodium propionate which is employed as a mold inhibitor.

We claim:

1. The process which comprises contacting at a temperature in the range of 200 C. to 550 C. a monoester of a dicar-boxylic acid wherein the ester radical is derived from a saturated hydrocarbon alcohol containing 1 to 7 carbon atoms and the acid radical is derived from an acid selected from the group consisting of maleic acid, succinic acid, fumaric acid, mesaconic acid, itaco-nic acid and citraconic acid with at least one catalytic compound selected from the group consisting of metal phosphates and metal oxides wherein the metal is selected from the group consisting of metals of groups I-B, I'I, IV, V-A, VI-B, VII-B and VIII of the periodic table in the presence of an excess of said alcohol and recovering an ester of a monocarboxylic acid.

2. The process of claim 1 wherein the process is carried out at a temperature in the range .of 250 C. to 400 C.

3. The process of claim 1 wherein the catalytic compound is an oxide of a group II metal.

4. The process for preparing methyl acrylate which comprises contacting at a temperature in the range of 250 C. to 400 C. monomethylmaleate with zinc oxide in the presence of excess methanol and recovering methyl 250 C. to 400 C. monomethyl maleate with magnesium oxide in the presence of excess methanol, and recovering methyl acrylate formed thereby.

6. A process for preparing methyl acrylate which comprises contacting at a temperature in the range of 250 C. to 400 C. monoethyl maleate with barium oxide in the presence of methanol, and recovering methyl acrylate formed thereby.

7. The process of claim 1 wherein the catalytic compound is an oxide of a group VIII metal.

8. A process for preparing methyl acrylate which comprises contacting at a temperature in the range of 250 C. to 400 C. monomethyl maleate with cobalt oxide in the presence of excess methanol, and recovering methyl acrylate formed thereby.

9. A process for preparing methyl acrylate which comprises contacting at a temperature in the range of 250 C. to 400 C. monomethyl maleate with nickel oxide in the presence of excess methanol, and recovering methyl acrylate formed thereby.

10. A process for preparing methyl acrylate which comprises contacting at a temperature in the range of 250 C. to 400 C. monomethyl maleate with iron oxide in the presence of excess methanol, and recovering methyl acrylate formed thereby.

11. The process of claim 1 wherein the catalytic compound is an oxide of a group VI-B metal.

12. A process for preparing methyl acrylate which comprises contacting at a temperature in the range of 250 C. to 400 C. monomethyl maleate with chromium :oxide in the presence of excess methanol, and recovering methyl acrylate formed thereby.

13. The process of claim 1 wherein the catalytic compound is a phosphate of a group XIII metal.

14. A process for preparing methyl acrylate which comprises contacting at a temperature in the range of 250 C. to 400 C. monomethyl maleate with iron phosphate in the presence of excess methanol, and recovering methyl acrylate formed thereby.

No references cited. 

1. THE PROCESS WHICH COMPRISES CONTACTING AT A TEMPERATURE IN THE RANGE OF 200*C. TO 550*C. A MONOESTER OF A DICARBOXYLIC ACID WHEREIN THE ESTER RADICAL IS DERIVED FROM A SATURATED HYDROCARBON ALCOHOL CONTAINING 1 TO 7 CARBON ATOMS AND THE ACID RADICAL IS DERIVED FROM AN ACID SELECTED FROM THE GROUP CONSISTING OF MALEIC ACID, SUCCINIC ACID, FUMARIC ACID, MESACONIC ACID, ITACONIC ACID AND CITRACONIC ACID WITH AT LEAST ONE CATALYTIC COMPOUND SELECTED FROM THE GROUP CONSISTING OF METAL PHOSPHATES AND METAL OXIDES WHEREIN THE METAL IS SELECTED FROM THE GROUP CONSISTING OF METALS OF GROUPS I-B, II, IV, V-A, VI-B, VII-B AND VIII OF THE PERIODIC TABLE IN THE PRESENCE OF AN EXCESS OF SAID ALCOHOL AND RECOVERING AN ESTER OF A MONOCARBOXYLIC ACID. 